Switching regulators for the conversion of electrical power are well known. Such switching regulators generally include various control circuits. Some circuits may be quite simple, such as a gate driver, others may be quite complex, such as the main control circuit.
Invariably, a control circuit requires a supply of power of its own. A supply for control circuits commonly goes by a name such as auxiliary supply, housekeeping supply, bias supply, VDD supply or VCC supply.
An auxiliary supply by itself requires a supply of current for operation. There is a general need for circuits providing the supply of current at lowest cost, smallest circuit size and highest efficiency.
A wide variety of circuits for the supply of current exist.
The suitability of some circuits depends on the operational stage of the switching regulator, the two states of main concern being the nonswitching or startup stage and the switching or running stage of switching regulator operation. The switching stage can be characterized by the stage of operation where control circuits are being prepared for switching operation of the switching regulator. The switching stage can be characterized by the stage where switching operation of the switching regulator is in place. Accordingly, some circuits are particularly suited to the nonswitching stage of switching regulator operation, whereas other circuits are particularly suited to the switching stage of switching regulator operation.
The suitability of some circuits depends on the configuration of the control circuit and its associated auxiliary supply within a switching regulator. Typically, a control circuit and its associated auxiliary supply are configured with a node in common. The potential at the common node may be broadly categorized as being one of two types, a steady voltage or a switching voltage. For instance, the main control circuit of a switching regulator and its associated auxiliary supply are typically configured with a common node carrying a steady potential. A gate driver of a floating switch within a switching regulator and its associated auxiliary supply are frequently configured with a common node carrying a switching potential. Accordingly, some circuits are particularly suited to a configuration with a common node carrying a steady potential. Other circuits are particularly suited to a configuration with a common node carrying a switching potential.
Among the more common circuits of the prior art for the supply of current is the supply by way of a resistor or a linear regulator, the supply by way of various transformer based techniques, and the supply by way of various switched capacitor techniques.
The supply of current by way of a resistor or a linear regulator is simple and low cost. This method is typically suited to the supply of current in both the nonswitching and switching stages of switching regulator operation, and is frequently suited to the supply of current for a configuration where the common node carries either a steady or a switching potential. The major drawback is the dissipation of power within the resistor or linear regulator. The dissipation becomes prohibitively large in offline switching regulators, thus requiring the use of other circuit solutions for the supply of current.
The supply of current by way of transformer techniques is more complicated but provides a supply of current with relatively high efficiency. This method typically relies on the switching operation of the switching regulator, and, therefore, is typically suited to the switching stage of switching regulator operation only. The method is generally suited to configurations where the common node carries either a steady or a switching voltage. A common drawback is a dependence of the auxiliary supply voltage on operating conditions of the switching regulator, such as loading, input voltage, or output voltage, the dependence at times requiring additional voltage regulation circuitry.
The supply of current by way of various switched capacitor techniques is generally low cost and efficient. A common configuration is the bootstrap supply. The bootstrap technique is typically suited to the switching stage of switching regulator operation only. The method is generally suited to configurations where the common node carries a switching voltage only.
What is needed is a circuit for the supply of current to an auxiliary supply that is suitable for use during the nonswitching and switching stages of switching regulator operation, and that is suitable for configurations with a common node carrying either steady or switching potential, and that has minimal power dissipation.